As John indicated the current version of the CSE and its documentation are installed with APL+Win v13.2.

The current version of the CSE documentation indicates:(a) The right argument to the CSE 'Exec' method must be a text array of rank 2. This is why you (correctly) received the 'invalid argument...' error message.(b) There is an additional CSE 'ExecStmt' method which is designed for a text vector (rank 1).

The following APL+Win statements comply with these CSE syntax requirements: